I haven't seen this topic discussed yet, so I wanted to bring it up.
Ultrasonic cleaners use a mechanical connection to transfer the "vibration" to the tank that then transfers to the liquid contained within it. Most have a cyclic rate of around 40Khz, although I've seen some in the 20K range as well. The generator portion of these devices are usually pretty small and are specifically engineered to do just what I described above and nothing more. This is why all the units come with a hanging basket, made of plastic or more preferably, stainless steel.
The reason I am mentioning this is because it appears many people are using these units by filling them up with water and sitting the bottles on the floor of the tank. Although it might be ok for a while, if you are putting 2-3 heavy glass bottles filled with 60ml each of juice, this puts a load on the generator that far exceeds it's design factors. This does 2 things. 1) depending on the size of the generator and the weight that you sit on the tank floor, it can slow the generator down and it will run at a lower frequency because of the extra weight and 2) because of the extra load, the generator mechanism will run hotter than normal... and we all know what excessive heat does to all things mechanical and electrical over time.
I am not sure what effect it would have on steeping with the generator running slower than it is meant to, other than possibly taking longer to do the same job. But it is almost all but certain that this extra load will shorten the lifespan of the unit overall. You may or may not really care if you have a 30 dollar Chinese unit, but just something to consider, especially if you went out and spent 150 bucks on a nice one. If you use plastic bottles and "float" them in the liquid, this would also negate this dampening effect as long as they don't migrate to the side and make/keep contact with the tank sides ( although this would have a much less dramatic effect on the unit than sitting weight on the floor of the tank).
I also wanted to add one more thing that could be found useful... if you have ever wondered if your US cleaner was actually DOING anything or working properly. It may be buzzing, but is it really working?
An easy way to test this is to take a small piece of aluminum foil strip and dip it into the cleaner when it is running. don't drop it in, let it hang. The cleaner should created a bunch of tiny holes in the foil or at least create a lot of really tiny dents, over a couple of minutes, the foil should start to completely deteriorate. If it does nothing, your unit is either not working, or the generator has become weak. Again, I am not sure if a "weak" generator would still steep your liquids or not, it may still work fine for that purpose, but it's cavitation abilities that dislodge particles for cleaning would be seriously affected at that point.
If you want to see this test, you can watch it here ==>
Ultrasonic Cleaner Foil Test | Ultrasonic Cleaning Machine Foil Test - YouTube